What Is Auto Scaling?

Auto Scaling helps you ensure that you have the correct number of EC2 instances available to handle
the load for your application. You create collections of EC2 instances, called
Auto Scaling groups. You can specify the minimum number of instances in
each Auto Scaling group, and Auto Scaling ensures that your group never goes below this size. You can
specify the maximum number of instances in each Auto Scaling group, and Auto Scaling ensures that your group
never goes above this size. If you specify the desired capacity, either when you create the
group or at any time thereafter, Auto Scaling ensures that your group has this many instances. If
you specify scaling policies, then Auto Scaling can launch or terminate instances as demand on your
application increases or decreases.

For example, the following Auto Scaling group has a minimum size of 1 instance, a desired capacity of
2 instances, and a maximum size of 4 instances. The scaling policies that you define adjust
the number of instances, within your minimum and maximum number of instances, based on the
criteria that you specify.

Auto Scaling Components

The following table describes the key components of Auto Scaling.

Groups

Your EC2 instances are organized into groups
so that they can be treated as a logical unit for the purposes
of scaling and management. When you create a group, you can specify
its minimum, maximum, and, desired number of EC2 instances. For more
information, see Auto Scaling Groups.

Launch configurations

Your group uses a launch configuration as a
template for its EC2 instances. When you create a launch configuration,
you can specify information such as the AMI ID, instance type, key pair,
security groups, and block device mapping for your instances. For more information,
see Launch Configurations.

Scaling plans

A scaling plan tells Auto Scaling when and how to scale. For example, you
can base a scaling plan on the occurrence of specified
conditions (dynamic scaling) or on a schedule. For more
information, see Scaling Plans.

Getting Started

To begin, complete the Getting Started with Auto Scaling tutorial to create an Auto Scaling group
and see how it responds when an instance in that group terminates. If you already have
running EC2 instances, you can create an Auto Scaling group using an existing EC2 instance,
and remove the instance from the group at any time. After you are familiar with how
Auto Scaling works, read Planning Your Auto Scaling Group to learn how to make the most of Auto Scaling.

Accessing Auto Scaling

AWS provides a web-based user interface, the AWS Management Console. If you've signed up for an AWS account,
you can access Auto Scaling by signing into the AWS Management Console. To get started, select EC2
from the console home page, and then select Launch Configurations
from the navigation pane.

If you prefer to use a command line interface, you have several options:

AWS Command Line Interface (CLI)

Provides commands for a broad set of AWS products, and is supported on Windows, Mac,
and Linux. To get started, see AWS Command Line Interface User Guide. For more information
about the commands for Auto Scaling, see autoscaling in the AWS Command Line Interface Reference.

Auto Scaling provides a Query API. These requests are HTTP or HTTPS requests that use the HTTP verbs GET or POST and a
Query parameter named Action. For more information about the API actions for Amazon EC2, see Actions in the Amazon EC2 API Reference.

If you prefer to build applications using language-specific APIs instead of
submitting a request over HTTP or HTTPS, AWS provides libraries, sample code, tutorials,
and other resources for software developers. These libraries provide basic functions that
automate tasks such as cryptographically signing your requests,
retrying requests, and handling error responses, making it is easier for you to get
started. For more information, see AWS SDKs and Tools.

For information about your credentials for accessing AWS, see
AWS Security Credentials
in the Amazon Web Services General Reference.

Pricing for Auto Scaling

There are no additional fees with Auto Scaling, so it's easy to try it out and see how it can
benefit your AWS architecture.

To monitor the calls made to the Auto Scaling API for your account, including calls made by the AWS Management Console,
command line tools, and other services, use AWS CloudTrail. For more information, see the AWS CloudTrail User Guide.